CH. 14 Cardiovascular System: Blood Vessels, Blood Flow, and Blood Pressure Flashcards
What two physical laws govern blood flow and blood pressure?
pressure gradients and resistance in the cardiovascular system
How is the circulatory system a closed system?
there is no input or output but is rather just constant
What is the equation for flow?
change in pressure/resistance
What drives flow from high pressure to low pressure in the cardiovascular system?
pressure gradients (bulk flow)
What is the change in pressure across the systemic circuit?
pressure in aorta (MVP) minus pressure in vena cava (CVP) just before it empties into right atrium
What is change in pressure across the pulmonary circuit?
pressure in pulmonary arteries minus pressure in pulmonary veins
T/F does blood in pulmonary circuit service the lungs
False; pulmonary circuit is meant only for gas exchange
Is the pressure gradient greater in the systemic circuit or pulmonary circuit?
systemic circuit; resistance in pulmonary circuit is much less than resistance through the systemic circuit
What three factors affect resistance to flow?
- radius of vessel
- length of vessel
- viscosity of fluid
What is blood viscosity dependent on?
amount of RBCs and proteins - usually constant
How does arteriole radius affect blood flow?
Vasoconstriction: decreased radius -> increased resistance
Vasodilation: increased radius -> decreased resistance
What is total peripheral resistance?
combined resistance of all blood vessels within the systemic circuit
What does vasoconstriction in network of blood vessels lead to?
increased resistance -> decreased flow
What does vasodilation in network lead to?
decreased resistance -> increased flow
How would you relate pressure gradients and resistance in the systemic circulation?
Flow = Cardiac output
Change in pressure = mean arterial pressure
Resistance = total peripheral resistance
How do arteries act as a pressure reservoir?
they have thick, elastic arterial walls that push blood through system
- expand during systole and recoil during diastole
What structural features make arteries a rapid transport pathway?
large diameter and little resistance
What is compliance? What is meant by low compliance and high compliance?
measure of how the pressure of a vessel will change with a change in volume
- Low compliance: small increase in blood volume causes a large increase in pressure
- High compliance: large increase in blood volume is required to produce a large increase in pressure
What is observed when measuring the blood pressure of a compressed artery?
turbulent flow produces Korotkoff sound
- pressure at first Korotkoff sound = systolic blood pressure
What is observed when measuring the blood pressure of an uncompressed artery?
laminar flow, no sound
- pressure when sound disappears = diastolic blood pressure
What is the equation for mean arterial pressure (MAP)?
MAP = [SP + (2 x DP)]/3
What are resistant vessels?
arterioles; connect arteries to capillaries or metarterioles
What factors affect arteriole radius?
- contraction state of smooth muscle in arteriole wall
- arteriolar tone: contraction level is independent of extrinsic influences
- vasoconstriction: increased contraction = decreased radius
- vasodilation: decreased contraction = increased radius
What are the two functions of varying arteriole radius?
- controlling blood flow to individual capillary beds
2. regulating mean arterial pressure
What is regulation of blood flow to organs based on?
need
What local factors control vascular resistance?
- changes in radius of arterioles
- depends on contractile state of smooth muscle in walls of the vessel
- local factors regulate, thereby regulate blood flow
What do changes associated with increased metabolic activity generally cause?
vasodilation
- carbon dioxide
- potassium
- hydrogen ions
What do changes associated with decreased metabolic activity generally cause?
vasoconstriction
- oxygen
What is active hyperemia?
increased blood flow in response to increased metabolic activity
What occurs as a result of active hyperemia in organs?
- increased metabolic rate
- response to low oxygen and high carbon dioxide
- increased blood flow
What is reactive hyperemia?
increased blood flow in response to a previous reduction in blood flow
What occurs when there is a blockage of blood flow to tissues?
metabolites increase and oxygen decreases but once blockage is released, metabolites are removed and oxygen is delivered as blood flow increases due to low resistance
What is a myogenic response?
change in vascular resistance in response to stretch of blood vessels in the absence of external factors
What is the purpose of myogenic auto-regulation of blood flow?
to keep blood flow constant
What are the big 4 local vasoactive substance and what are their effects on vascular smooth muscle?
- oxygen: vasoconstriction
- carbon dioxide: vasodilation
- potassium ions: vasodilation (vasoconstriction at high concentrations)
- acids (hydrogen ions): vasodilation
How is blood distributed during exercise?
- Dilation of vessels to skeletal muscle and heart increases blood flow to muscles
- Constriction of vessels to GI tract and kidneys decreases blood flow to these organs
What is mean arterial pressure dependent on?
total peripheral resistance
What is total peripheral resistance dependent on?
radius of arterioles
What extrinsic mechanisms regulate the radius of arterioles to control MAP?
- sympathetic activity
2. hormones
How doe TPR and MAP increase when arteriolar radius is under sympathetic control?
norepinephrine binds to alpha adrenergic receptors and vasoconstriction is produced
What adrenergic receptors are present in arterioles to skeletal and cardiac muscle?
both alpha and beta 2 receptors
What binds to alpha adrenergic receptors and what occurs?
norepinephrine binds to alpha receptors and vasoconstriction occurs
What binds to both alpha and beta 2 receptors and what occurs?
epinephrine binds to both
- vasoconstriction at alpha receptors
- vasodilation at beta 2 receptors
What adrenergic receptor does epinephrine have a greater affinity for?
beta 2 receptors
What effect do sympathetic nerves have on arteriole radius?
vasoconstriction
What effect does epinephrine have on arteriole radius?
alpha adrenergic: vasoconstriction
beta 2 adrenergic: vasodilation
What effect does vasopressin have on arteriole radius?
vasoconstriction
What effect does angiotensin II have on arteriole radius?
vasoconstriction
Which blood vessel has the slowest velocity of blood flow?
capillaries; slow blood flow enhances exchange between blood and tissue
What is allowed to move through continuous capillaries?
small water soluble molecules
What is allowed to move through fenestrated capillaries?
proteins, and in some cases blood cells
What are metarterioles and what do they function as?
they are intermediate between arterioles and capillaries that directly connect arterioles to venules
- function as shunts to bypass capillaries
What does contraction and relaxation of the smooth muscle of metarterioles do?
contraction: decrease blood flow through capillaries
relax: increase blood flow through capillaries
What are pre-capillary sphincters?
rings of smooth muscle that surround capillaries on the arteriole end
- only contract and relax in response to local factors
What does contraction and relaxation of pre-capillary sphincters do?
contraction: constricts capillary which decreases blood flow
relaxation: increases blood flow
What is the most common mechanism to exchange across capillary walls?
diffusion
- lipophilic: across membrane
- lipophobic: through channels
What are the 3 ways that exchange can occur across capillary walls?
- diffusion
- transcytosis: exchangeable proteins
- mediated transport: in brain
What kind of movement is filtration across capillaries?
Movement out of capillary into interstitial space
What kind of movement is absorption across capillaries?
Movement into capillary from interstitial space
What are the 4 starling forces across the capillary walls?
- Capillary hydrostatic pressure
- Interstitial fluid hydrostatic pressure
- Capillary osmotic pressure
- Interstitial fluid osmotic pressure
What is the equation for net filtration pressure?
NFP = filtration pressure - absorption pressure
What is the role of the lymphatic system during blood circulation?
picks up excess filtrate and cleans and returns it to circulation
What are some factors that affect filtration and absorption across capillaries?
- standing on feet - increases hydrostatic pressure
- injuries
- when capillaries are damaged, they leak fluid and proteins
- histamine increases capillary permeability to proteins - liver disease
- decreases plasma proteins
- not enough plasma proteins lowers level of reabsorption - kidney disease
- heart disease
What are venules?
connect capillaries to veins with little smooth muscle in walls
What allows unidirectional blood flow in veins and where are they present?
valves
- present in peripheral veins
- absent from central veins
What makes veins compliant vessels?
- expand with little change in pressure
- function as blood reservoir
- 60% of the total blood volume in systemic veins are at rest
What 4 factors influence venous pressure and venous return?
- skeletal muscle pump: one way valves in peripheral veins
- blood moves toward heart when contracted
- blood flows into veins between muscles when relaxed - respiratory pump:
- inspiration decreases pressure in thoracic and increases pressure in abdominal
- pressure in abdominal creates favorable gradient for movement to thoracic - blood volume
- increased blood volume -> increased venous pressure
- decreased blood volume -> decreased venous pressure - venomotor tone: smooth muscle tension in the veins
- increases central venous pressure
- decreases venous compliance
- increases venous return
What is the smooth muscle in the walls of veins innervated by?
sympathetic nervous system
What hormone acting at the alpha adrenergic receptors causes venous constriction?
norepinephrine
Where do lymphatic veins drain lymph fluid?
into the thoracic duct which empties into the right atrium
What are the three determinants of mean arterial pressure (MAP)?
- heart rate
- stroke volume
- total peripheral resistance
What causes hypotension?
mean arterial pressure is less than normal and is caused by inadequate blood flow to tissues
What causes hypertension?
mean arterial pressure is greater than normal and is a stressor for heart and blood vessels when prolonged
How is mean arterial pressure regulated in the short term?
primarily neural control that regulates cardiac output and total peripheral resistance
- involves the heart and blood vessels
How is mean arterial pressure regulated in the long term?
primarily hormonal control that regulates blood volume and involves the kidneys
Lay out the negative feedback loop used in neural regulation of mean arterial pressure.
Detector = baroreceptors
Integration center = cardiovascular centers in the brainstem
Controllers = autonomic nervous system
Effectors = heart and blood vessels
What are baroreceptors?
pressure receptors that respond to stretching due to pressure changes in arteries
What are the two arterial baroreceptors?
aortic arch and carotid sinuses
What is the cardiovascular control center comprised of?
medulla oblongata which is the integration center for blood pressure regulation
What is the input (5) and output (2) of the cardiovascular control center?
Input:
- arterial baroreceptors
- low pressure baroreceptors
- chemoreceptors (oxygen and carbon dioxide)
- proprioceptors
- higher brain centers
Output:
- sympathetic nervous system
- parasympathetic nervous system
What occurs during autonomic output to cardiovascular effectors?
Parasympathetic input to SA node (decreases HR) -> AV node
Sympathetic input to SA node (increases HR) -> AV node -> ventricular myocardium (increases contractility) -> Arterioles (increases resistance) -> Veins (increases venomotor tone)
What is the framework of maintaining blood pressure at normal level?
baroreceptor reflex
- Detectors - baroreceptors
- Afferents - visceral afferents
- Integration center - cardiovascular control center
- Efferents - autonomic nervous system
- Effectors - heart, arterioles, and veins
What 3 hormones provide long term mean arterial pressure regulation?
- epinephrine
- vasopressin
- angiotensin II
How does epinephrine increase mean arterial pressure?
- acts on smooth muscle of arterioles (increases TPR)
- acts on smooth muscle of veins (increases venomotor tone)
- acts on heart (increases HR and SV)
How do vasopressin and angiotensin II regulate mean arterial pressure?
vasoconstrictors that increase TPR and MAP
What do low-pressure baroreceptors do and where are they found?
decrease in blood volume activates receptors which trigger responses that act in parallel with the baroreceptor reflex
- found in walls of large systemic veins and walls of atria
How does respiratory sinus arrhythmia regulate heart rate?
during inspiration:
- sympathetic activity increases -> heart rate increases
during expiration:
- parasympathetic activity increases -> heart rate decreases
What effect do chemoreceptors have on ventilation when carbon dioxide levels are increased in the blood?
carbon dioxide increases which in turn increases TPR and decreases HR
- MAP generally increases
How is thermoregulation mediated and how does it regulate cardiovascular responses?
through hypothalamus
- an increase in body temperature leads to: decrease sympathetic activity to skin
- vasodilation to skin
- increase heat loss to environment
What is more important to cardiovascular regulatory responses: baroreceptor reflex or thermoregulation?
thermoregulation
